1. Technical Field
The present disclosure relates to radiofrequency amplifiers that use phase-shifted full bridge resonant inverters. Particularly, the present disclosure is directed to improving the efficiency and dynamic range of radiofrequency amplifiers.
2. Background of the Related Art
Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryogenic, thermal, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. A source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated and the return electrode is placed remotely from the active electrode to carry the current back to the generator. In bipolar electrosurgery, one of the electrodes of the hand-held instrument functions as the active electrode and the other as the return electrode.
Electrosurgical generators may use a phase-shifted full bridge resonant inverter to generate the electrosurgical energy needed to perform the electrosurgical procedure. One example of a resonant inverter uses a LCLC tank topology driven by an H-bridge having two pairs of field effect transistors (FETs). Each pair of FETs includes two FETs that are connected in series. The two serially connected FETs should not be switched on at the same time or a short circuit would occur at the input voltage source. In order to avoid the short circuit, a fixed dead-time is provided between the pulse applied to the first FET and the pulse applied to the second FET among the pair of FETs. Depending on the load conditions of the resonant inverter, the optimal dead-times may also vary. If the dead-times of the FETs are too large or too short relative to the optimal dead-times, then the FET transition will be partially in zero-voltage switching and partially hard-switching. As the FETs hard-switch to a greater extent, the efficiency of the resonant inverter drops dramatically.